Valerie,
I'm willing to bet that what you've described is Fuligo septica
(unofficial "common" name: the "dog-barf slime"), a slime mold (not a
true fungus, but an interesting organism with some animal
characteristics and some fungal ones). This creature is pretty common in
bark mulch and garden areas. It's not harmful to plants, pets, or
people, and the plasmodial stage (the bright yellow, "blob" that crawls
around) can be kept as a "pet" in culture and fed oatmeal.